This invention relates to distance measuring devices, and more specifically to a retro-reflective prism assembly and target for use with electronic distance measuring instruments.
In the last several years, optical surveying equipment has evolved to where infrared and laser optical systems are used in conjunction with electronic distance measuring systems, typically in civil engineering applications such as surveying. These electronic distance measuring systems provide range and angular information with respect to remotely located reflecting devices which can be placed up to several kilometers from the measuring instrument.
The early type of measuring systems used a telescope or theodolite rigidly mounted to a support, such as a tripod. A "mount-on" ranging system was also mounted to the same support as the theodolite, with the optical paths of the ranging system and the theodolite being parallel, but offset by a known distance. A retro-reflector was mounted above the target, such that alignment of the theodolite with the target aligned the ranging system with the retro-reflector. In this type of measuring system, the targets were stationary and the accuracy of the ranging system was degraded, or unworkable, if the target was mounted so as to tile with the retro-reflector. More recently, the alignment theodolite optics and the ranging optics have been designed as to be coaxial. With this coaxial system, sometimes referred to as a "total station," it is preferred that the target tilt with the retro-reflector. since the tilting target/retro-reflector is not suitable for the "mount-on" ranging system, a different retro-reflector typically had to be used for each type of electronic measuring system.
There is thus a need for a remote target and retro-reflector that can be used with both the "mount-on" and the coaxial types of electronic distance measuring systems.
These electronic distance measuring instruments usually consist of two main components, an emitter/receiver, and a remote reflector. The emitter/receiver transmits either infrared or laser energy to a remotely placed reflector assembly which reflects the energy back to a receiver which in turn is connected to an electronic calculating system.
The remote reflectors typically comprise retro-reflecting prisms, such as corner cubes, which have reflecting optics that reflect incident energy on a path that is colinear with the incident energy. Unfortunately, the sensitivity of the receiving portion of the electronic distance measuring instruments usually requires that the remote reflector be adjusted to be substantially perpendicular or normal to the incoming energy. Thus, the remote reflector prism should be positioned in both azimuth and elevation to permit the user to adjust the reflector until it is substantially normal to the incoming energy, and thereby enable the receiver to work at its optimum capacity.
To facilitate initial alignment, a target is sometimes placed adjacent the remote reflector. These targets tend to take the form of rods with alternating red and white stripes, or targets with black and white stripes converging at, or directed towards, the center of the target. As described previously, in some systems the targets are often mounted adjacent to, and sometimes connected to, the reflecting prism.
The remote reflecting prisms are sometimes designed to be "plunged," which refers to the ability to rotate the reflecting prism 180.degree. about a horizontal axis so that the prism can be redirected to point in substantially the opposite direction, without moving the support on which the remote reflector prism is mounted.
There is presently no easy way to allow the remote reflecting prism to be plunged if the prism is connected to a target. The support for the remote reflecting prisms may allow a combined target and prism to rotate, but not to rotate sufficiently to plunge the prism. This rotational limitation is especially pronounced if a large target is used, or if the target surrounds a portion of the prism.
There is thus a need for the remote reflecting prism which can be plunged while simultaneously providing a sufficient target area, or other alignment means, to facilitate quick alignment of the remote reflecting prism with the emitter/receiver.
It is thus an object of this invention to provide a means for plunging both the target and prism assembly, simultaneously, in either direction about a single rotational axis.
It is further an object of this invention to provide a target which substantially surrounds the prism, and has the center of the target at the optical axis of the prism assembly.
It is an additional object of this invention to provide a target having a targeting surface on both sides of the target.
It is still a further object of this invention to provide course alignment indicators, as well as more precise alignment indicators so as to allow quick and easy alignment of the optical axis.